Apparatus with labyrinth heat exchanger for the sputtering depositionof thin films

ABSTRACT

SPUTTERING APPARATUS IS IMPROVED BY PROVIDING THE CATHODE THEREOF WITH AN INTEGRALLY FORMED GRADED LABYLINTH HEAT EXCHANGER THROUGH WHICH A COOLANT IS CIRCULATED TO MAINTAIN THE CATHODE AND TARGET MATERIAL AT A UNIFORM TEMPERATURE. COOLANT PARTS AND POWER INPUT PROVISIONS ARE MADE SUCH THAT THE SPUTTERING CHAMBER MAY BE HERMETICALLY SEALED WITH A SINGLE SEAL.

July 24, 1973 c PROVENZANO ET AL 3,748,253

APPARATUS WITH LABYRIN'IH HEAT nxcrmucm von THE SPUTTERING DEPOSITION OF THIN FILMS Filed Jan. 24, 1972 2 Sheets-Sheet 1 I I l 71 7/ I I V SUPPLY TO VACUUM PUMP AND INERT GAS FIG.

July 24, 1973 J. c. PROVENZANO E 3,743,253 I APPARATUS WITH LABYRINTH HEAT EXCHA R FOR THE SPUTTERING DEPOSITION OF THIN FILMS 2 Sheets-Sheet 2 Filed Jan. 24, 1972 United States Patent 3,748,253 APPARATUS WITH LABYRINTH HEAT EX- CHANGER FOR THE SPUTTERING DEPOSI- HON 0F THIN FILMS Joseph C. Provenzano, Glenview, and Richard E.

Govednik, Schaumhurg, Ill., assignors to GTE Automatic Electric Laboratories Incorporated, Northlake,

' Filed Jan. 24, 1972, S91. No. 220,242

Int. Cl. C23c 15/00 US. Cl. 204-298 7 Ciaims ABSTRACT OF THE DISCLOSURE Sputtering apparatus is improved by providing the cathode thereof with an integrally formed graded labyrinth heat exchanger through which a coolant is circulated to maintain the cathode and target material at a uniform temperature. Coolant parts and power input provisions are made such that the sputtering chamber may be hermetically sealed with a single seal.

BACKGROUND OF THE INVENTION The deposition of thin films of a variety of materials by the process known as sputtering is well known. Typically a cathode is provided with a layer of sputtering or target material and the substrate on which the material is to be deposited forms an anode. The anode and cathode are hermetically sealed in a vacuum chamber containing an inert gas. A high potential is applied across the anode and cathode to deposit the sputtering material on the substrate. Since the target material receives on the order of 95% of the input power in a vacuum, its temperature will rise to unacceptable levels unless cooling is provided. The high temperature target material tends to radiantly heat the fixtures used in the apparatus which results in the release of contaminant gases into the vacuum chamber. This outgassing of contaminants may cause uncontrollable sputtering plasma changes which degrade the quality of the deposited thin films.

Cooling may be provided, however, it is important that the target material temperature be maintained as uniform as possible in order that non-uniformities in sputtering rates at different portions of the surface are avoided. Typically, in prior art sputtering apparatus the coolant input and output hoses as well as the electrical power input were introduced through the vacuum side of the sealed chamber through separate seals thus constituting significant points of potential failure while the apparatus was operated under a high vacuum.

OBJECTS AND SUMMARY OF THE INVENTION From the preceding discussion it will be understood that among the various objectives of the present invention are included:

The provision of new and improved apparatus for the sputter deposition of thin films;

The provision of apparatus of the above-described character having improved target material cooling provisions; and

The provision of apparatus of the above-described character having an improved hermetic sealing arrangement.

These and other objectives of the present invention are efiiciently achieved by providing the cathode on which target material to be sputtered is carried with an integrally formed graded labyrinth through which a coolant may be circulated to uniformly cool the cathode surface to a selected temperature. Coolant inlet and outlet lines as well as the electrical power input are provided through the 3,748,253 Patented July 24, 1973 'ice structure of the heat exchanging cathode such that the vacuum chamber may be sealed with a single seal.

The foregoing as well as other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Turning to FIG. 1 there is illustrated a sputtering apparatus including a generally circular base plate 10 having a central aperture through which a sputtering cathode 12 may be inserted. A vacuum chamber 22 is provided by any suitable means such as the illustrated bell jar 21 hermetically sealed to the base plate 10 in seals 23. The cathode 12 is held in a sputtering flange 14 which is secured to the underside of the base plate 10 by a collar 16. The cathode 12 is supported in a spaced relationship with respect to the sputtering flange 14 by a plurality of ceramic positioning and spacing stand-offs 18 such that an inert gas such as helium introduced through a gas inlet 20 may circulate around the cathode 12 and into the vacuum chamber 22. The cathode is further provided with an integrally formed graded labyrinth 24 through which a suitable coolant may be circulated via inlet and outlet couplings 26 and 28 respectively. The labyrinth is more clearly shown in the horizontal cross-section view of the cathode in FIG. 2. A coolant entering the labyrinth at the inlet port 30 flows radially outward through passage 32, semi-circumferentially through passages 34 back via return passage 35 and exits via the outlet port 36. It will be noted that graded spacing of circumferential passages 34; i.e., spacing between passages increases with radial distance from the center of the cathode; allows the maintenance of the cathode at a uniform temperature. The recesses 38 adapted to receive the ceramic stand-offs 18 of FIG. 1 are illustrated in phantom.

The sputtering cathode 12 is positioned in the sputtering flange 14 by the stand oifs I8 and first and second electrically insulative spacers 40 and 42 fixed to the sputtering flange 14 by bolts 44. A first dielectric O ring 46 is disposed in a recess in the upper surface of the first spacer 40. The second spacer 4-2 is provided with a beveled inner edge adapted to receive a second dielectric O ring 48 which provides hermetic sealing of the vacuum chamber 22 from the environment. Once in proper position the cathode I2 is held in place by first and second dielectric jam nuts 45 and 47 threaded on the lower end of the cathode 12 pulling it down against a spacer 49 between the second spacer 42 and the first jam nut 45.

The upper surface of the base plate 10 is provided with a substrate holder 50 carried by a holder support 52 on bearings 54 such that the holder 50 may be driven in rotation about its longitudinal axis. The provision for driving the substrate holder 50 is schematically illustrated as a motor 56 having a friction wheel 58 which engages the periphery of the holder 50. A plurality of thin film substrates 60 are retained in a frame 62 fixed to the underside of the holder 50. An electrically conductive post 64 is disposed through the substrate holder 50 and in electrical contact with the substrate retaining frame 62. Electrical contact with the post 64 is made through a spring 3 contact 66 which is coupled to the base plate which is maintained at ground potential.

The configuration of a typical substrate retaining frame 62 will be more clearly understood from the horizontal view of FIG. 3. The frame 62 is provided with a plurality of apertures which receive and retain the substrates 60 on which thin films are to be deposited. A plurality of mounting holes 68 are provided through which the frame is fixed to the holder 54) and a central aperture 70 is provided to receive and engage the conductive post 64.

In operation of layer of sputtering or target material 72 is placed on the upper surface of the cathode 12, the chamber 22 is evacuated and an inert atmosphere introduced. The power is then applied from a suitable supply 74 to the cathode 12, and the substrate holder rotating motor 56 is actuated in order that an even deposition of target material is provided.

It \m'll be noted from the illustrated construction of the sputtering cathode 12 that the complete cooling system for the apparatus is at the atmosphere side of the vacuum chamber 22 and that hermetic sealing is efiiciently achieved through the use of the dielectric O ring 48. By integrally forming the coolant inlet/outlet passages and heat exchange labyrinth 24 in the structure of the sputtering cathode 12 a significant potential failure point has been eliminated while uniform cooling of the target material is maintained. It will thus be apparent that the applicants have provided an apparatus whereby the objectives set forth hereinabove are efficiently achieved. Since certain changes in the above-described construction will occur to those skilled in the art without departure from the scope of the invention it is intended that all matter contained in the foregoing description or shown in the appended drawings shall be interpreted as illustrative and not in a limiting sense.

Having described what is new and novel and desired to secure by Letters Patent, what is claimed is:

1. Improved apparatus for the sputter deposition of materials on substrates comprising a vacuum chamber,

an electrically conductive cathode structure disposed partially within said vacuum chamber, adapted to receive on its upper surface a layer of target material to be sputtered and having integrally formed therein coolant inlet and outlet ports and a graded labyrinth heat exchanger in communication with said inlet and outlet ports,

said graded labyrinth heat exchanger comprising a first radially extending inlet passage, a second radially extending outlet passage and a plurality of substantially concentric semi-circumferential passages in direct communication with said first and second radially extending passages,

means for hermetically sealing said cathode structure to said vacuum chamber,

a substrate holder disposed vertically adjacent said cathode structure and adapted to be driven in horizontal rotation,

means for driving said substrate holder in rotation,

means for coupling said substrate holder to ground potential, and

a source of electrical power coupled to said cathode structure.

2. Apparatus as recited in claim 1 wherein the distance between adjacent circumferential passages is increasingly greater with radial distance from the center of said cathode structure.

3. Apparatus as recited in claim 1 wherein said means for coupling said substrate holder to ground potential comprises an electrically conductive post disposed substantially through the center of said substrate holder and adapted to rotate therewith, and a spring loaded electrical contact engaging said post and coupled to ground potential.

4. Apparatus as recited in claim 3 wherein said substrate holder comprises an electrically non-conductive basket, and an electrically conductive substrate retaining frame having a plurality of apertures therein each adapted to receive and retain a substrate upon which target material is to be deposited, said frame being aflixed to the under surface of said basket and rotating therewith, and

said electrically conductive post extending through said basket and being electrically continuous with said substrate retaining frame.

5. Apparatus as recited in claim 1 wherein said vacuum chamber comprises a base plate having a centrally disposed aperture therein and a bell jar hermetically sealed to said base plate enclosing said aperture, said cathode structure extending through and electrically isolated from said base plate and further including means for retaining said cathode structure in a fixed spatial relationship with respect to said base plate.

6. Apparatus as recited in claim 5 wherein said cathode structure retaining means comprises an electrically conductive flange affixed to the underside of said vacuum chamber base plate and having a central aperture and a plurality of recesses disposed in the interior horizontal surface thereof about said aperture,

said cathode structure extending through said aperture in said flange and having a like plurality of recesses disposed in the horizontal under surface thereof,

a plurality of electrically insulative stand oifs disposed in said recesses to thereby electrically isolate said cathode structure from said base plate and said flange and retain said cathode structure in a fixed spatial relationship with respect thereto,

electrically insulative means for securing said cathode structure in position against said stand ofis, and

a dielectric O ring disposed between said cathode structure and said securing means to thereby hermetically seal said cathode structure to said vacuum chamber.

7. Apparatus as recited in claim 1 further including means for introducing a selected gaseous atmosphere into said vacuum chamber.

References Cited UNITED STATES PATENTS 3,649,512 3/1972 Ackley 204298 3,528,906 9/1970 Cash 204298 3,625,858 12/1971 Snaper 204-298 3,532,615 10/1970 Davidse et al. 204l92 3,681,227 8/1972 Szupillo 204-192 3,595,775 7/1971 Grantham et a1. 204-298 3,502,562 3/1970 Humphries 204192 JOHN H. MACK, Primary Examiner y S. S. KANTER, Assistant Examiner US. Cl. X.R. 118-69 

